It is known to add hydrazine compounds to photographic silver halide emulsions or developing solutions. For example, the addition of hydrazine compounds to photographic silver halide emulsions or developing solutions is disclosed in U.S. Pat. No. 3,730,727 (a developing solution containing a combination of ascorbic acid with hydrazine), U.S. Pat. No. 3,227,552 (the use of hydrazine as an auxiliary developing agent to obtain a direct positive color image), U.S. Pat. No. 3,386,831 (silver halide photographic material containing .beta.-monophenyl hydrazides of aliphatic carboxylic acids as stabilizers), U.S. Pat. No. 2,419,975 and Mees, The Theory of Photographic Process, the third edition (1966), page 281.
Among them, U.S. Pat. No. 2,419,975 discloses that a high-contrast negative image can be obtained by adding hydrazine compounds.
It is disclosed in the aforesaid U.S. Pat. No. 2,419,975 that very high-contrast photographic characteristics having a gamma (.gamma.) value higher than 10 can be obtained when a hydrazine compound is added to a silver chlorobromide emulsion and development is carried out with a developing solution having a pH of as high as 12.8. However, a strongly alkaline developing solution having a pH of nearly 13 is likely to be oxidized by air, and hence the developing solution is unstable and can not withstand the storage or the use over a long period of time.
Attempts have been made to obtain a high-contrast image by developing silver halide photographic materials containing hydrazine compounds with a developing solution having a lower pH.
JP-A-1-179939 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-1-179940 (these applications correspond to EP324,426A) disclose a processing method wherein photographic materials containing a nucleating development accelerator having an adsorptive group to silver halide grains and a nucleating agent having an adsorptive group are developed with a developing solution having a pH of not higher than 11.0. However, when the amounts of the compounds having an adsorptive group added to silver halide emulsions exceed a critical amount, there are the problems that light sensitivity is deteriorated, development is restrained, and the compounds interfere with the effect of other useful adsorptive additives. Accordingly, the amount of the compound having an adsorptive group to be added is limited to a certain range, and a sufficiently high contrast can not be achieved.
U.S. Pat. Nos. 4,998,604 and 4,994,365 disclose hydrazine compounds having a repeating unit derived from ethylene oxide and hydrazine compounds having a pyridinium group. However, as is clear from Examples of the above patent specification, high contrast is not sufficient, and there is a difficulty in obtaining high contrast and necessary Dmax under practical processing conditions.
JP-A-60-140340 discloses that a high contrast can be obtained by adding an amine into a silver halide photographic material. However, when a developer having a pH of lower than 11.0 is used for development of this photographic material, a sufficient high contrast cannot be achieved.
JP-A-56-106244 discloses that a high contrast can be achieved by adding an amino compound into a developer having a pH of 10 to 12. However, when the developer is used there occur troubles with respect to smell, stain which occurs by adhering of the amino compound to an apparatus for processings, or environmental pollutions. Even though it has been demanded to incorporate such compounds into a photographic material, compounds which provide sufficient effects by incorporating them into a photographic material have not been found.
JP-A-61-47943 and JP-A-61-47949 disclose photographic materials containing hydrazines and sensitizing dyes selected from thiohydantoins. However, high contrast can be obtained only when photographic materials containing the sensitizing dyes and the hydrazines in combination are developed with a developing solution having a pH of higher than 11. High contrast can not be obtained by using a developing solution having a lower pH as intended by the present invention, namely, by using a developing solution having a pH of not higher than 11.
As mentioned above, sufficient high contrast could not be obtained when conventional photographic materials were developed with a developing solution having a pH of not higher than 11.